1. Field of the Invention
The present invention relates to a power conversion device including a switching circuit and a control circuit.
2. Description of the Related Art
As a power conversion device including a switching circuit and a control circuit, for example, an on-board direct current-to-direct current (DC-DC) converter disclosed in JP-B-4198677 is known.
The on-board DC-DC converter includes a DC-DC converter and a controller. The DC-DC converter has a metal-oxide-semiconductor (MOS) power transistor. The controller repeats a plurality of pulse signals having differing cycles in a predetermined sequence, and outputs the pulse signals as switching signals. In other words, the controller changes switching frequency of the switching signals in a predetermined pattern. In addition, the controller repeats the changes in the predetermined pattern at every repetition time. As a result, the switching frequencies are dispersed. Therefore, compared to when the switching frequency is fixed, the maximum value of the power spectrum can be suppressed. As a result, noise interfering with radios can be reduced.
However, in the above-described on-board DC-DC converter, a power spectrum is newly generated that corresponds with a repetition frequency that is the inverse of the repetition time. When the repetition frequency is in a frequency band that can be demodulated as sound by a radio, abnormal noise is generated from the radio. A problem occurs in that passengers in the vehicle experience discomfort.